The present invention relates to an electric connection box which includes an insulated case and a bus bar substrate stored in the interior portion of the insulated case.
An electric connection box is used to branch connect a wireharness for a car to various electric parts; specifically, with use of the electric connection box, the branch connecting points of the wireharness can be collected together at a given portion to thereby be able to arrange the reasonable and economical wiring for the branch connecting points. The electric connection box is structured such that a bus bar substrate composed of an insulating plate and a band-shaped metal plate disposed on the insulating plate is stored in the interior portion of an insulated case. With the enhanced density of the wireharness, there have been developed various kinds of electric connection boxes according to types of cars or according to uses. Also, a mechanical relay, which serves as switching means for turning on/off a given electronic circuit, is carried on the outer surface of the insulated case as the need arises.
FIG. 5 is an exploded perspective view of the main portions of an electric connection box with such mechanical relay carried thereon. In this electric connection box, a relay socket 104, which is disposed on the outer surface of an insulated case 101, is connected through relay terminals 105 to a plurality of tab terminals 103 provided on and projected from the upper surface of a bus bar substrate 102 which is stored in the interior portion of the insulated case 101, and a mechanical relay 106 is mounted on the relay socket 104.
By the way, in the case of the bus bar substrate 102, to mount the mechanical relay 106 on the relay socket 104, the plurality of tab terminals 103, which are respectively formed by bending the leading end portions of a plurality of (for example, three) bus bars, must be disposed such that they are situated adjacently to each other. Due to this, there arises the need that the plurality of bus bars must be divided into a plurality of (at least two) layers in order to be able to prevent the bus bars from interfering with each other, which unfavorably results in the complicated structure of the bus bar substrate 102. Owing to this, the manufacturing process of the bus bar substrate 102 is complicated to thereby put a limit on reduction of the manufacturing cost of the product (that is, the electric connection box).
Also, in the field of cars, recently, there has been popular a tendency that cars are manufactured in large kinds and in small lots and thus, in some cases, an on/off control circuit using the mechanical relay 106 must be changed so as to have a circuit configuration which requires different types of bus bars depending on the kinds of cars. In such case, there is newly required an expensive metal mold which is used to mold these bus bars. This not only puts a limit on reduction of the product (electric connection box) manufacturing cost but also requires the time for manufacturing the new metal mold to thereby delay the start of manufacture of a new product (electric connection box)
By the way, there is also known a structure in which electronic circuit units each including a control circuit disposed upwardly of the bus bar substrate 102 are disposed in layers or stages; and, by configuring an on/off control circuit using the mechanical relay 106 on such electronic circuit unit, there can be avoided the need to change the shapes of the bus bars in the bus bar substrate 102. However, in this case, not only there is required a new print wiring substrate for configuring the electronic circuit unit but also there arises the need to change a connector which is used to connect together the bus bar substrate 102 and the electronic circuit unit; that is, substantially, there arises a similar problem found in the previously described conventional structure.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional electric connection boxes. Accordingly, it is an object of the invention to provide an electric connection box which not only can simplify the structure of a bus bar substrate to thereby facilitate the assembling of the bus bar substrate but also is able to easily cope with a change in a circuit configuration.
In attaining the above object, according to a first aspect of the invention, there is provided an electric connection box, comprising an insulated case and a bus bar substrate including a bus bar circuit thereon and stored in the interior portion of the insulated case, the bus bar circuit being composed of an insulated plate and a bus bar formed of a metal plate and disposed on at least the surface of the insulated plate, wherein the present electric connection box further comprises a switching element having a plurality of external terminals, and the switching element is incorporated into the bus bar circuit through the external terminals in such a state that the switching element is surface mounted on the bus bar substrate.
According to this structure, since the switching element to be incorporated into the bus bar circuit is surface mounted on the bus bar substrate, supply of a drive voltage to the switching element as well as input and output of an electric signal between the switching element and bus bar substrate can be carried out through connecting means such as a wire which is disposed on the surface of the bus bar substrate. Thanks to this, there is avoided the need to raise a tab terminal for relay connection up from the bus bar as in the conventional electric connection box, which not only can simplify the structure of the bus bar substrate to thereby facilitate the assembling of the bus bar substrate but also allows the bus bar substrate and thus the electric connection box to cope with a change in a circuit configuration easily.
Also, according to a second aspect of the invention, in an electric connection box as set forth in the first aspect of the invention, the switching element is surface mounted on the bus bar of the bus bar substrate.
According to this structure, even in case where the switching element is an element which generates heat, heat generated by the switching element is transmitted directly to the metal-made bus bar which is high in thermal conductivity and is then radiated into the external space through the bus bar. Thanks to this, excessive heat generation by the switching element can be prevented more positively, which makes it possible to realize an electric connection box showing excellent operation reliability.
Also, according to a third aspect of the invention, in an electric connection box as set forth in the second aspect of the invention, the switching element includes an external terminal on the mounting surface thereof and this external terminal is connected directly to the bus bar.
According to this structure, a wiring member such as a wire can be omitted and the external terminal on the mounting surface of the switching element can be connected to the bus bar positively, thereby being able to realize an electric connection box which has a high heat radiating effect and also shows excellent operation reliability.
And, according to a fourth aspect of the invention, in an electric connection box as set forth in the second or third aspect of the invention, the bus bar includes heat radiating means which is used to radiate heat generated from the switching element into the external space.
According to this structure, Joule heat generated from the switching element is radiated into the external space through the heat radiating means. This can enhance the heat radiating property of the switching element, thereby being able to realize an electric connection box showing more excellent operation reliability.
Also, according to a fifth aspect of the invention, in an electric connection box as set forth in the fourth aspect of the invention, the heat radiating means is composed of a heat radiating member including a fin and at least part of the fin is exposed to the outside of the insulated case.
According to this structure, Joule heat generated from the switching element is effectively radiated into the external space of the insulated case through the fin having a large heat radiating area. This can enhance the heat radiating property of the switching element further, thereby being able to realize an electric connection box showing still more excellent operation reliability.
And, according to a sixth aspect of the invention, in an electric connection box as set forth in any one of the first to fifth aspect of the invention, the switching element is structured such that at least part of the external terminals are connected to the bus bar substrate through wires.
According to this structure, supply of a drive voltage to the switching element to be surface mounted onto the bus bar substrate as well as input and output of an electric signal between the switching element and bus bar substrate are carried out through the wires. This not only can simplify the structure of the bus bar substrate to thereby facilitate the assembling of the bus bar substrate but also allows the bus bar substrate and thus the electric connection box to cope with a change in a circuit configuration easily.
Also, according to a seventh aspect of the invention, in an electric connection box as set forth in the sixth aspect of the invention, at least part of the wire, on the bus bar substrate, is sealed by an insulated coating member.
According to this structure, since the wire is restricted on the bus bar substrate side, when a car starts or stops suddenly, the vibrations of the wire with respect to the bus bar substrate can be controlled. This can prevent the wire from being cut, thereby being able to realize an electric connection box showing excellent operation reliability. Especially, in case where the insulated coating member has elasticity or visco-elasticity, the vibrations of the wire applied when a car starts or stops suddenly can be effectively absorbed by the insulated coating member, which makes it possible to effectively reduce stresses caused in the wire.
And, according to an eighth aspect of the invention, in an electric connection box as set forth in any one of the first to seventh aspects of the invention, a print circuit is integrally disposed on part of the surface of the bus bar substrate and at least part of the external terminals of the switching element are connected to the print circuit.
According to this structure, input and output of an electric signal between the switching element and print circuit are carried out through the connecting means such as a wire. This not only can simplify the structure of the bus bar substrate to thereby facilitate the assembling of the bus bar substrate but also allows the bus bar substrate and thus the electric connection box to cope with a change in a circuit configuration easily.